The present invention relates in general to an illumination device such as a flashlight and the like, and more particularly, to such an illumination device having an adjustable beam focus.
Flashlights of varying sizes and shapes are well-known in the art. In particular, certain of these known flashlights utilize two or more dry cell batteries as their source of electrical energy carried in series in a cylindrical housing serving as a handle for the flashlight. The actuation of a switch completes a circuit within the housing to enable electrical current to pass through the filament of a bulb, thereby generating light which is typically focused by a reflector to form a beam of light.
The production of light from such flashlights has often been degraded by the quality of the reflector utilized and the optical characteristics of any lenses interposed in the beam path. Efforts at improving such flashlights have primarily addressed the quality of the optical characteristics. The production of more highly reflective, well-defined reflectors, which may be incorporated within such flashlights have been found to provide a more well-defined focus thereby enhancing the quality of the light being produced.
Since there exists a wide variety of uses for hand-held flashlights, one desirable feature is the capability of adjusting the beam width, i.e., variable focus which produces a beam of light having a variable dispersion. In certain situations it is useful to provide a concentrated beam of light of constant diameter, while in other circumstances, it is desirable for the beam to spread and thereby illuminate a larger area. This has been achieved in the past by selecting the position of the bulb with respect to the parabolic reflector commonly used in flashlights.
The bulb is located at the focus of a parabolic reflector and rays from the bulb are collimated by the reflector to provide a beam which is of substantially constant diameter. On the other hand, a beam that is conical in shape, i.e., one that spreads, has been achieved by moving the bulb so as not to be located at the focus of the reflector. The distance between the bulb location and the focus point will effect the amount of beam spread or dispersion. Flashlights that have had this capability in the past have generally included a large number of components and complicated mechanisms, all of which have rendered these flashlights relatively expensive to manufacture.
Varying the relative position of the bulb with respect to the focus point of the reflector has been achieved by a number of designs. For example, there is known from U.S. Pat. No. 3,689,759 the longitudinal movement of the bulb by means of an internal motor which drives a supporting shaft. U.S. Pat. No. 2,945,944 slides an internal battery casing within its outer housing. U.S. Pat. No. 2,239,928 provides an adjustable threaded rod attached to a bracket supporting the bulb holder. U.S. Pat. No. 4,533,984 provides a central knob which receives the front end of the bulb in a spring biased assembly U.S. Pat. No. 3,603,783 utilizes an exterior magnet which effects a magnetic member which is secured to the bulb housing. U.S. Pat. No. 2,516,993 achieves longitudinal movement of the bulb by means of a slide plate. U.S. Pat. No. 3,875,397 provides a manually rotatable bulb housing. U.S. Pat. No. 4,414,612 achieves longitudinal movement of the bulb housing which is connected to a carriage by means of an externally accessible tab. U.S. Pat. No. 3,196,268 utilizes a switch which when depressed causes a dog to push against a lip resulting in the bulb housing moving rearward U.S. Pat. No. 4,841,417 achieves longitudinal movement of a bulb housing by rotation of a housing tail assembly. Additionally, U.S. Pat. Nos. 4,527,223, 4,577,263, 4,821,156, 4,388,673 and 4,656,565 achieve beam focusing by rotation of a head assembly which supports the parabolic reflector.
Despite the apparent variety of construction details to achieve variable beam focusing in a flashlight, there still remains a need for an internal assembly having few components and which is economical to manufacture.